In general, an X-ray tube device including an emitter having a flat plate-like electron emission portion is known. Such an X-ray tube device is disclosed in National Patent Publication Gazette No. 2010-534396, for example.
An X-ray tube device disclosed in the aforementioned National Patent Publication Gazette No. 2010-534396 includes an emitter including a flat plate-like electron emission portion and a pair of (two) terminal portions connecting the electron emission portion and an electrode to each other. An anisotropic polycrystalline material (tungsten) having a long crystal structure is employed for the electron emission portion. The terminal portions support the lower surface (a surface opposite to an electron emission surface) of the flat plate-like electron emission portion in the vicinity of both ends and have a function of applying an electric current to the electron emission portion. The electron emission portion is applied with an electric current through the terminal portions to be heated to at least about 2000° C., whereby the electron emission portion emits an electron. Therefore, the electron emission portion is creep-deformed by a high temperature associated with the use of the emitter and external force acting on the electron emission portion. In the aforementioned National Patent Publication Gazette No. 2010-534396, the electron emission portion is configured such that the longitudinal direction of crystal grains is oriented in a prescribed direction, and the mechanical strength of the electron emission portion in the direction (a direction parallel to the electron emission surface) of action of principal stress loading in normal use is improved. Thus, a deterioration of the electron emission characteristics of the emitter and a reduction in the lifetime of the emitter resulting from the creep deformation are suppressed.